The evolution of a universe with $\Omega =1\mathrm{}$ which becomes dominated by relatively light, nonintercommuting strings at red shift $z_s$ is similar to that of a matter-dominated universe with $\Omega \sim {(2+z_s)}^{-1\mathrm{}}<1\mathrm{}$. The existence of such strings can resolve the conflict between the $\Omega =1\mathrm{}$ prediction of inflationary cosmology and observations.

• Received 1 June 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.1016